Melting Glaciers Trigger Growing Risk of Lake Tsunamis in Alaska and Beyond

As global temperatures rise, melting glaciers are not only contributing to sea-level rise but also increasing the risk of lake tsunamis in regions with mountain glaciers, such as Alaska and British Columbia. These tsunamis, triggered by landslides into small bodies of water, have mostly occurred in remote locations so far. However, geologist Bretwood Higman of Ground Truth Alaska warns that it may just be a matter of time before a tsunami swamps a more populated place like Portage Lake near Whittier, Alaska.

Assessing the Risk of Lake Tsunamis

At the Seismological Society of America (SSA)’s 2024 Annual Meeting, Higman discussed the importance of assessing sites like Portage Lake for the possibility of lake tsunamis, in part by using distinctive seismic signals connected to landslides. “There are some cases where there are dramatic and very distinctive precursory seismic signals that precede a catastrophic landslide, sometimes by as much as days,” Higman noted. “If we could get to the point where we understood these and knew how to detect them, they could be really useful.”

Higman calls lake tsunamis “an emerging, climate-linked hazard.” The geological conditions that underlie these events in places like Alaska are usually similar. Higher temperatures melt the glaciers that buttress the walls of the valley that cradles the shrinking glacier. Without the glacier in place to hold them up, the valley walls are more prone to landslide, either into an existing body of water or a new lake created by the glacier melt. In other areas, warming conditions are weakening permafrost that may be important to the stability of slopes above lakes.

Learning from Remote Events to Prepare for Future Tsunamis

The 2020 Elliot Creek tsunami in a glacial valley in British Columbia, for instance, featured a landslide measuring 18 cubic million meters in volume and a tsunami runup of more than 100 meters. While forest and salmon habitat were the main casualties of that tsunami, Higman and his colleagues are studying these remote but dramatic events to find ways to prepare for tsunamis in places with more infrastructure. “There are places where we see the same kinds of geologic instability that preceded these other events, but there are a lot of people exposed,” said Higman.

Higman also noted that there are some parallels between the tectonic faults that seismologists usually study and “the behaviors that we’re seeing in the failure surface of these very large landslides,” suggesting that they also offer one way to study fault dynamics in miniature.

As climate change continues to impact glaciers and permafrost, the risk of lake tsunamis is expected to grow. Identifying high-risk areas and developing early warning systems based on seismic signals could help protect communities and infrastructure from these potentially devastating events. By studying the mechanisms behind lake tsunamis and learning from remote occurrences, scientists like Higman aim to better understand and mitigate the risks associated with this emerging hazard.

Keyword: lake tsunamis

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